1. Field of the Invention
The present invention is generally related to angular position sensors and, more particularly to a throttle position sensor that uses two gear tooth sensors in combination with a rotating gear tooth pattern.
2. Description of the Prior Art
In certain applications, such as in conjunction with a throttle body or carburetor, it is necessary to determine the angular position of the throttle plate so that an electronic engine control unit can make appropriate decisions to control the operation of the engine. Whenever an engine control unit, or ECU, is used to control the operation of an internal combustion engine, it is necessary to provide some type of feedback signal so that the engine control unit is able to know the actual angular position of the throttle. Several types of angular position sensors are known to those skilled in the art. One type utilizes a wiper contact that is slidable over a resistor that is shaped either in the form of a coil or a film resistor arranged in a serpentine pattern. Rotation of the shaft attached to a throttle plate causes the wiper contact to change the resistance and, as a result, the output voltage from the angular position sensor.
A noncontact type of angular position sensor, with decreased sensitivity to shaft position variability is described in U.S. Pat. No. 5,164,668, which issued to Alfors on Nov. 17, 1992. The sensor provided with first and second pole pieces that extend from regions proximate a rotatable magnet to regions proximate a magnetically sensitive device. The pole pieces provide defined magnetic paths of lowered reluctance that confine the lines of flux extending between the rotatable magnet and the magnetically sensitive device. The placement of the rotatable magnet between first and third pole pieces of the invention significantly reduces the sensitivity of the sensor to variations in position of the rotatable magnet and therefore increases the reliability of the measurement system. This reduced sensitivity inhibits the degradation of operational accuracy that could otherwise be caused by inaccuracies in the magnet's position, large tolerances in the dimensions of the shaft diameter and the bearing diameter and, in addition, the variable location of the shaft because of excessive bearing wear.
U.S. Pat. No. 5,140,262, discloses a gear tooth sensor with a center line and non intersecting relation with the center of rotation of a rotatable member. The off axis gear tooth sensor is provided with a centerline of the sensor disposed along a line which is not coincidence with the center of rotation of the rotatable member to be sensed. Instead, the centerline of the housing in which the Hall Effect element is disposed is positioned at a perpendicular distance from the center of rotation of the rotatable member which is determined as the function of a range of dimensions which define the allowable gap between the Hall Effect element and a surface of a rotatable member. The perpendicular distance between the center of rotation and the line along which the proximity sensor is disposed is mathematically determined as a function of a distance between the center of rotation of the rotatable member and the minimum and maximum possible locations of the Hall Effect element along the angular distance between those two dimensions.
U.S. Pat. No. 5,304,926, which issued on Apr. 19, 1994, to Wu, discloses a gear tooth position sensor with two Hall Effect elements. The position sensor has two magnetically sensitive devices associated with a magnet. The sensor is disposable proximate a rotatable member having at least one discontinuity in its surface. The two magnetically sensitive devices, such as Hall Effect transducers, each provide output signals that represent the direction and magnitude of the magnetic field in which its respective transducer is disposed. An algebraic sum of the first and second output signals from the magnetically sensitive devices is provided as an indication of the location of the rotatable member that is disposed proximate the sensor.
In certain applications, such as outboard motors for marine use, the throttle position sensors experience significant vibration. As a result, the life of the throttle position sensor is decreased because of the excessive vibration. Several alternative actions can be taken to limit the disadvantages caused by the excessive vibration, but it would be significantly beneficial if a means could be developed for sensing the throttle position without requiring angular position sensors that are subject to excessive wear as a result of the vibrations normally associated with an outboard motor.